(Not Applicable)
1. Field of the Invention
This invention relates to an electronic article surveillance (EAS) system and more specifically to EAS systems which generate a reduced number of false detection alarms.
2. Description of the Relevant Art
Electronic Article Surveillance (EAS) systems are detection systems that allow the identification of a marker or tag within a given detection region. EAS systems have many uses, but most often they are used as security systems for preventing shoplifting in stores or removal of property in office buildings. EAS systems come in many different forms and make use of a number of different technologies.
A typical EAS system includes an electronic detection unit, markers and/or tags, and a detacher or deactivator. The detection units can, for example, be formed as pedestal units, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The markers and/or tags have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active marker passes through a marker detection region, the EAS system sounds an alarm, a light is activated, and/or some other suitable alert devices are activated to indicate the removal of the marker from the proscribed area.
Common EAS systems operate using the same general principles using a transmitter and a receiver. Typically the transmitter is placed on one side of the detection region and the receiver is placed on the opposite side of the detection region. The transmitter produces a predetermined exciter signal in a marker detection region. In the case of a retail store, this detection region is usually formed at a checkout aisle or an exit. When an EAS marker enters the detection region, the marker has a characteristic response to the exciter signal which can be detected. For example, the marker may respond to the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating resonators. This characteristic response is subsequently detected by the receiver. By design, the characteristic response of the marker is distinctive and not likely to be created by natural circumstances.
EAS systems are often called upon for coverage of a large detection area, such as a mall store entrance. The mall store entrance can sometimes cover the width of the mall store itself. Such relatively large detection areas require special design considerations. For example, the EAS system used for coverage must be carefully designed to avoid any gaps through which a marker might pass through undetected, while simultaneously avoiding false alarming caused by markers attached to store inventory which may be displayed near the detection region. The condition in which the detection region extends into the confines of the store in this manner is called xe2x80x9cover-range.xe2x80x9d
When there is over-range in an EAS system, markers attached to clothes or other goods within a store will produce the expected characteristic response and resulting false alarming. These false alarms, resulting from tags too close to the placement of the EAS system, cause problems within the store and generate unwanted service calls for tuning the EAS system.
In stores where the rental price per square foot is high, false alarms generated by over-ranging of the EAS system is problematic and expensive because it wastes valuable retail floor space. It is thus desirable to develop an EAS system that has the ability to adequately cover a wide exit area without the problems posed by over-ranging.
It is an object of the present invention to provide an EAS system with a wide exit coverage area.
It is also an object of the present invention to provide an EAS system with reduced over-range.
It is further an object of the present invention to provide an EAS system with reduced false alarms.
It is an additional object of the present invention to provide an EAS system that requires a reduced number of service calls.
These and other objects of the present invention are achieve by a subject apparatus for detecting an identification marker in a detection area of an electronic article surveillance system. The system includes a transmitter for transmitting an exciter pulse for exciting an identification marker, and a receiver system for receiving a characteristic response energy emitted by an identification marker in an inhibit field of the detection zone and in a main area of said detection zone. A comparator is provided for generating an alarm condition when the characteristic response energy received in the main area exceeds the characteristic response energy received in the inhibit field by a predetermined threshold value. The apparatus according to claim 1, wherein said receiver system comprises at least one inhibit field antenna for receiving energy in said inhibit field and at least one main antenna for receiving energy in said main area.
According to one aspect, the system includes more than one inhibit field antennas and a more than one main field antennas. In this case, the energy in the inhibit field antennas is combined in an inhibit receiver channel and the energy in the main field antennas is combined in a main field receiver channel. According to another aspect of the invention, the inhibit field antennas can be located above and below the detection zone. Similarly, the main field antennas can be located above and below the detection zone. The transmitter antenna is positioned so that the exciter pulse will excite markers in the main field and the inhibit field. According to one embodiment, the transmitter can be located between the inhibit field antenna and the main field antenna.
The transmitter antenna can be a loop antenna or any other suitable design. By comparison, the inhibit field antenna and the main field antenna are preferably directional ferrite type antennas. However, other types of antennas such as a loop antenna may also be used for this purpose.
According to another aspect of the invention, a filter is provided for removing received characteristic response energy originating from markers which are stationary. This filter can be implemented as a time delay filter wherein the delay time applied is equivalent to an integer number of transmit cycles of the transmitter.
According to another aspect, the invention can include a method for detecting an identification marker in a detection zone of an electronic article surveillance system. The method includes the steps of transmitting an exciter pulse for exciting an identification marker, receiving a characteristic response energy emitted by an identification marker in an inhibit field of said detection zone or in a main area of said detection zone, and generating an alarm condition when the characteristic response energy received in the main area exceeds the characteristic response energy received in the inhibit field by a predetermined threshold value.
The method can further include the steps of providing one or more inhibit field antennas for receiving energy in the inhibit field and one or more main field antenna for receiving energy in the main area. If multiple main field and inhibit field antennas are used, the method can also include the step of combining in an inhibit receiver channel the energy received from the inhibit field antennas and combining in a main receiver channel energy from the main field antennas. According to one aspect of the method, the inhibit field antennas are preferably positioned above and below said detection zone. Similarly, the main field antennas can be positioned above and below said detection zone. The transmitter antenna is advantageously positioned in a location such that markers in both the main field and inhibit field will be excited. For example, the transmitter antenna may be located between the inhibit field antenna and the main field antenna.
The method can further include the step of removing characteristic response energy for markers which are stationary. This can be accomplished for example by passing the received characteristic response energy through a time delay filter. In that case, the delay time applied by the time delay filter should be equivalent to an integer number of transmit cycles of exciter pulses.